10 files changed, 951 insertions, 0 deletions
diff --git a/lang/lua/astal/binding.lua b/lang/lua/astal/binding.lua
new file mode 100644
index 0000000..ba1e6e4
--- /dev/null
+++ b/lang/lua/astal/binding.lua
@@ -0,0 +1,71 @@
+local lgi = require("lgi")
+local GObject = lgi.require("GObject", "2.0")
+
+---@class Binding
+---@field emitter table|Variable
+---@field property? string
+---@field transformFn function
+local Binding = {}
+
+---@param emitter table
+---@param property? string
+---@return Binding
+function Binding.new(emitter, property)
+    return setmetatable({
+        emitter = emitter,
+        property = property,
+        transformFn = function(v)
+            return v
+        end,
+    }, Binding)
+end
+
+function Binding:__tostring()
+    local str = "Binding<" .. tostring(self.emitter)
+    if self.property ~= nil then
+        str = str .. ", " .. self.property
+    end
+    return str .. ">"
+end
+
+function Binding:get()
+    if self.property ~= nil and GObject.Object:is_type_of(self.emitter) then
+        return self.transformFn(self.emitter[self.property])
+    end
+    if type(self.emitter.get) == "function" then
+        return self.transformFn(self.emitter:get())
+    end
+    error("can not get: Not a GObject or a Variable " + self)
+end
+
+---@param transform fun(value: any): any
+---@return Binding
+function Binding:as(transform)
+    local b = Binding.new(self.emitter, self.property)
+    b.transformFn = function(v)
+        return transform(self.transformFn(v))
+    end
+    return b
+end
+
+---@param callback fun(value: any)
+---@return function
+function Binding:subscribe(callback)
+    if self.property ~= nil and GObject.Object:is_type_of(self.emitter) then
+        local id = self.emitter.on_notify:connect(function()
+            callback(self:get())
+        end, self.property, false)
+        return function()
+            GObject.signal_handler_disconnect(self.emitter, id)
+        end
+    end
+    if type(self.emitter.subscribe) == "function" then
+        return self.emitter:subscribe(function()
+            callback(self:get())
+        end)
+    end
+    error("can not subscribe: Not a GObject or a Variable " + self)
+end
+
+Binding.__index = Binding
+return Binding
diff --git a/lang/lua/astal/file.lua b/lang/lua/astal/file.lua
new file mode 100644
index 0000000..e3be783
--- /dev/null
+++ b/lang/lua/astal/file.lua
@@ -0,0 +1,45 @@
+local lgi = require("lgi")
+local Astal = lgi.require("AstalIO", "0.1")
+local GObject = lgi.require("GObject", "2.0")
+
+local M = {}
+
+---@param path string
+---@return string
+function M.read_file(path)
+    return Astal.read_file(path)
+end
+
+---@param path string
+---@param callback fun(content: string, err: string): nil
+function M.read_file_async(path, callback)
+    Astal.read_file_async(path, function(_, res)
+        local content, err = Astal.read_file_finish(res)
+        callback(content, err)
+    end)
+end
+
+---@param path string
+---@param content string
+function M.write_file(path, content)
+    Astal.write_file(path, content)
+end
+
+---@param path string
+---@param content string
+---@param callback? fun(err: string): nil
+function M.write_file_async(path, content, callback)
+    Astal.write_file_async(path, content, function(_, res)
+        if type(callback) == "function" then
+            callback(Astal.write_file_finish(res))
+        end
+    end)
+end
+
+---@param path string
+---@param callback fun(file: string, event: integer): nil
+function M.monitor_file(path, callback)
+    return Astal.monitor_file(path, GObject.Closure(callback))
+end
+
+return M
diff --git a/lang/lua/astal/gtk3/app.lua b/lang/lua/astal/gtk3/app.lua
new file mode 100644
index 0000000..7895f69
--- /dev/null
+++ b/lang/lua/astal/gtk3/app.lua
@@ -0,0 +1,96 @@
+local lgi = require("lgi")
+local Astal = lgi.require("Astal", "3.0")
+local AstalIO = lgi.require("AstalIO", "0.1")
+
+local AstalLua = Astal.Application:derive("AstalLua")
+local request_handler
+
+function AstalLua:do_request(msg, conn)
+    if type(request_handler) == "function" then
+        request_handler(msg, function(response)
+            AstalIO.write_sock(conn, tostring(response), function(_, res)
+                AstalIO.write_sock_finish(res)
+            end)
+        end)
+    else
+        Astal.Application.do_request(self, msg, conn)
+    end
+end
+
+function AstalLua:quit(code)
+    Astal.Application.quit(self)
+    os.exit(code)
+end
+
+local app = AstalLua()
+
+---@class StartConfig
+---@field icons? string
+---@field instance_name? string
+---@field gtk_theme? string
+---@field icon_theme? string
+---@field cursor_theme? string
+---@field css? string
+---@field hold? boolean
+---@field request_handler? fun(msg: string, response: fun(res: any))
+---@field main? fun(...): unknown
+---@field client? fun(message: fun(msg: string): string, ...): unknown
+
+---@param config StartConfig | nil
+function Astal.Application:start(config)
+    if config == nil then
+        config = {}
+    end
+
+    if config.client == nil then
+        config.client = function()
+            print('Astal instance "' .. app.instance_name .. '" is already running')
+            os.exit(1)
+        end
+    end
+
+    if config.hold == nil then
+        config.hold = true
+    end
+
+    request_handler = config.request_handler
+
+    if config.css then
+        self:apply_css(config.css)
+    end
+    if config.icons then
+        self:add_icons(config.icons)
+    end
+    if config.instance_name then
+        self.instance_name = config.instance_name
+    end
+    if config.gtk_theme then
+        self.gtk_theme = config.gtk_theme
+    end
+    if config.icon_theme then
+        self.icon_theme = config.icon_theme
+    end
+    if config.cursor_theme then
+        self.cursor_theme = config.cursor_theme
+    end
+
+    app.on_activate = function()
+        if type(config.main) == "function" then
+            config.main(table.unpack(arg))
+        end
+        if config.hold then
+            self:hold()
+        end
+    end
+
+    local _, err = app:acquire_socket()
+    if err ~= nil then
+        return config.client(function(msg)
+            return AstalIO.send_message(self.instance_name, msg)
+        end, table.unpack(arg))
+    end
+
+    self:run(nil)
+end
+
+return app
diff --git a/lang/lua/astal/gtk3/astalify.lua b/lang/lua/astal/gtk3/astalify.lua
new file mode 100644
index 0000000..065de40
--- /dev/null
+++ b/lang/lua/astal/gtk3/astalify.lua
@@ -0,0 +1,236 @@
+local lgi = require("lgi")
+local Astal = lgi.require("Astal", "3.0")
+local Gtk = lgi.require("Gtk", "3.0")
+local GObject = lgi.require("GObject", "2.0")
+local Binding = require("astal.lib.binding")
+local Variable = require("astal.lib.variable")
+local exec_async = require("astal.lib.process").exec_async
+
+local function filter(tbl, fn)
+    local copy = {}
+    for key, value in pairs(tbl) do
+        if fn(value, key) then
+            if type(key) == "number" then
+                table.insert(copy, value)
+            else
+                copy[key] = value
+            end
+        end
+    end
+    return copy
+end
+
+local function map(tbl, fn)
+    local copy = {}
+    for key, value in pairs(tbl) do
+        copy[key] = fn(value)
+    end
+    return copy
+end
+
+local flatten
+flatten = function(tbl)
+    local copy = {}
+    for _, value in pairs(tbl) do
+        if type(value) == "table" and getmetatable(value) == nil then
+            for _, inner in pairs(flatten(value)) do
+                table.insert(copy, inner)
+            end
+        else
+            table.insert(copy, value)
+        end
+    end
+    return copy
+end
+
+local function includes(tbl, elem)
+    for _, value in pairs(tbl) do
+        if value == elem then
+            return true
+        end
+    end
+    return false
+end
+
+local function set_children(parent, children)
+    children = map(flatten(children), function(item)
+        if Gtk.Widget:is_type_of(item) then
+            return item
+        end
+        return Gtk.Label({
+            visible = true,
+            label = tostring(item),
+        })
+    end)
+
+    -- remove
+    if Gtk.Bin:is_type_of(parent) then
+        local ch = parent:get_child()
+        if ch ~= nil then
+            parent:remove(ch)
+        end
+        if ch ~= nil and not includes(children, ch) and not parent.no_implicit_destroy then
+            ch:destroy()
+        end
+    elseif Gtk.Container:is_type_of(parent) then
+        for _, ch in ipairs(parent:get_children()) do
+            parent:remove(ch)
+            if ch ~= nil and not includes(children, ch) and not parent.no_implicit_destroy then
+                ch:destroy()
+            end
+        end
+    end
+
+    -- TODO: add more container types
+    if Astal.Box:is_type_of(parent) then
+        parent:set_children(children)
+    elseif Astal.Stack:is_type_of(parent) then
+        parent:set_children(children)
+    elseif Astal.CenterBox:is_type_of(parent) then
+        parent.start_widget = children[1]
+        parent.center_widget = children[2]
+        parent.end_widget = children[3]
+    elseif Astal.Overlay:is_type_of(parent) then
+        parent:set_child(children[1])
+        children[1] = nil
+        parent:set_overlays(children)
+    elseif Gtk.Container:is_type_of(parent) then
+        for _, child in pairs(children) do
+            if Gtk.Widget:is_type_of(child) then
+                parent:add(child)
+            end
+        end
+    end
+end
+
+local function merge_bindings(array)
+    local function get_values(...)
+        local args = { ... }
+        local i = 0
+        return map(array, function(value)
+            if getmetatable(value) == Binding then
+                i = i + 1
+                return args[i]
+            else
+                return value
+            end
+        end)
+    end
+
+    local bindings = filter(array, function(v)
+        return getmetatable(v) == Binding
+    end)
+
+    if #bindings == 0 then
+        return array
+    end
+
+    if #bindings == 1 then
+        return bindings[1]:as(get_values)
+    end
+
+    return Variable.derive(bindings, get_values)()
+end
+
+return function(ctor)
+    function ctor:hook(object, signalOrCallback, callback)
+        if GObject.Object:is_type_of(object) and type(signalOrCallback) == "string" then
+            local id
+            if string.sub(signalOrCallback, 1, 8) == "notify::" then
+                local prop = string.gsub(signalOrCallback, "notify::", "")
+                id = object.on_notify:connect(function()
+                    callback(self, object[prop])
+                end, prop, false)
+            else
+                id = object["on_" .. signalOrCallback]:connect(function(_, ...)
+                    callback(self, ...)
+                end)
+            end
+            self.on_destroy = function()
+                GObject.signal_handler_disconnect(object, id)
+            end
+        elseif type(object.subscribe) == "function" then
+            local unsub = object.subscribe(function(...)
+                signalOrCallback(self, ...)
+            end)
+            self.on_destroy = unsub
+        else
+            error("can not hook: not gobject+signal or subscribable")
+        end
+    end
+
+    function ctor:toggle_class_name(name, on)
+        Astal.widget_toggle_class_name(self, name, on)
+    end
+
+    return function(tbl)
+        if tbl == nil then
+            tbl = {}
+        end
+
+        local bindings = {}
+        local setup = tbl.setup
+
+        -- collect children
+        local children = merge_bindings(flatten(filter(tbl, function(_, key)
+            return type(key) == "number"
+        end)))
+
+        -- default visible to true
+        if type(tbl.visible) ~= "boolean" then
+            tbl.visible = true
+        end
+
+        -- collect props
+        local props = filter(tbl, function(_, key)
+            return type(key) == "string" and key ~= "setup"
+        end)
+
+        -- collect signal handlers
+        for prop, value in pairs(props) do
+            if string.sub(prop, 0, 2) == "on" and type(value) ~= "function" then
+                props[prop] = function()
+                    exec_async(value, print)
+                end
+            end
+        end
+
+        -- collect bindings
+        for prop, value in pairs(props) do
+            if getmetatable(value) == Binding then
+                bindings[prop] = value
+                props[prop] = value:get()
+            end
+        end
+
+        -- construct, attach bindings, add children
+        local widget = ctor()
+
+        if getmetatable(children) == Binding then
+            set_children(widget, children:get())
+            widget.on_destroy = children:subscribe(function(v)
+                set_children(widget, v)
+            end)
+        else
+            if #children > 0 then
+                set_children(widget, children)
+            end
+        end
+
+        for prop, binding in pairs(bindings) do
+            widget.on_destroy = binding:subscribe(function(v)
+                widget[prop] = v
+            end)
+        end
+
+        for prop, value in pairs(props) do
+            widget[prop] = value
+        end
+
+        if type(setup) == "function" then
+            setup(widget)
+        end
+
+        return widget
+    end
+end
diff --git a/lang/lua/astal/gtk3/init.lua b/lang/lua/astal/gtk3/init.lua
new file mode 100644
index 0000000..6fb5455
--- /dev/null
+++ b/lang/lua/astal/gtk3/init.lua
@@ -0,0 +1,5 @@
+return {
+    App = require("astal.gtk3.app"),
+    astalify = require("astal.gtk3.astalify"),
+    Widget = require("astal.gtk3.widget"),
+}
diff --git a/lang/lua/astal/gtk3/widget.lua b/lang/lua/astal/gtk3/widget.lua
new file mode 100644
index 0000000..beaad6c
--- /dev/null
+++ b/lang/lua/astal/gtk3/widget.lua
@@ -0,0 +1,90 @@
+local lgi = require("lgi")
+local Astal = lgi.require("Astal", "3.0")
+local Gtk = lgi.require("Gtk", "3.0")
+local astalify = require("astal.gtk3.astalify")
+
+local Widget = {
+    astalify = astalify,
+    Box = astalify(Astal.Box),
+    Button = astalify(Astal.Button),
+    CenterBox = astalify(Astal.CenterBox),
+    CircularProgress = astalify(Astal.CircularProgress),
+    DrawingArea = astalify(Gtk.DrawingArea),
+    Entry = astalify(Gtk.Entry),
+    EventBox = astalify(Astal.EventBox),
+    -- TODO: Fixed
+    -- TODO: FlowBox
+    Icon = astalify(Astal.Icon),
+    Label = astalify(Gtk.Label),
+    LevelBar = astalify(Astal.LevelBar),
+    -- TODO: ListBox
+    Overlay = astalify(Astal.Overlay),
+    Revealer = astalify(Gtk.Revealer),
+    Scrollable = astalify(Astal.Scrollable),
+    Slider = astalify(Astal.Slider),
+    Stack = astalify(Astal.Stack),
+    Switch = astalify(Gtk.Switch),
+    Window = astalify(Astal.Window),
+}
+
+Gtk.Widget._attribute.css = {
+    get = Astal.widget_get_css,
+    set = Astal.widget_set_css,
+}
+
+Gtk.Widget._attribute.class_name = {
+    get = function(self)
+        local result = ""
+        local strings = Astal.widget_get_class_names(self)
+        for i, str in ipairs(strings) do
+            result = result .. str
+            if i < #strings then
+                result = result .. " "
+            end
+        end
+        return result
+    end,
+    set = function(self, class_name)
+        local names = {}
+        for word in class_name:gmatch("%S+") do
+            table.insert(names, word)
+        end
+        Astal.widget_set_class_names(self, names)
+    end,
+}
+
+Gtk.Widget._attribute.cursor = {
+    get = Astal.widget_get_cursor,
+    set = Astal.widget_set_cursor,
+}
+
+Gtk.Widget._attribute.click_through = {
+    get = Astal.widget_get_click_through,
+    set = Astal.widget_set_click_through,
+}
+
+local no_implicit_destroy = {}
+Gtk.Widget._attribute.no_implicit_destroy = {
+    get = function(self)
+        return no_implicit_destroy[self] or false
+    end,
+    set = function(self, v)
+        if no_implicit_destroy[self] == nil then
+            self.on_destroy = function()
+                no_implicit_destroy[self] = nil
+            end
+        end
+        no_implicit_destroy[self] = v
+    end,
+}
+
+Astal.Box._attribute.children = {
+    get = Astal.Box.get_children,
+    set = Astal.Box.set_children,
+}
+
+return setmetatable(Widget, {
+    __call = function(_, ctor)
+        return astalify(ctor)
+    end,
+})
diff --git a/lang/lua/astal/init.lua b/lang/lua/astal/init.lua
new file mode 100644
index 0000000..f442db0
--- /dev/null
+++ b/lang/lua/astal/init.lua
@@ -0,0 +1,27 @@
+local lgi = require("lgi")
+local Binding = require("astal.binding")
+local File = require("astal.file")
+local Process = require("astal.proc")
+local Time = require("astal.time")
+local Variable = require("astal.variable")
+
+return {
+    Variable = Variable,
+    bind = Binding.new,
+
+    interval = Time.interval,
+    timeout = Time.timeout,
+    idle = Time.idle,
+
+    subprocess = Process.subprocess,
+    exec = Process.exec,
+    exec_async = Process.exec_async,
+
+    read_file = File.read_file,
+    read_file_async = File.read_file_async,
+    write_file = File.write_file,
+    write_file_async = File.write_file_async,
+    monitor_file = File.monitor_file,
+
+    require = lgi.require,
+}
diff --git a/lang/lua/astal/process.lua b/lang/lua/astal/process.lua
new file mode 100644
index 0000000..b8b7436
--- /dev/null
+++ b/lang/lua/astal/process.lua
@@ -0,0 +1,78 @@
+local lgi = require("lgi")
+local Astal = lgi.require("AstalIO", "0.1")
+
+local M = {}
+
+---@param commandline string | string[]
+---@param on_stdout? fun(out: string): nil
+---@param on_stderr? fun(err: string): nil
+---@return { kill: function } | nil proc
+function M.subprocess(commandline, on_stdout, on_stderr)
+    if on_stdout == nil then
+        on_stdout = function(out)
+            io.stdout:write(tostring(out) .. "\n")
+        end
+    end
+
+    if on_stderr == nil then
+        on_stderr = function(err)
+            io.stderr:write(tostring(err) .. "\n")
+        end
+    end
+
+    local proc, err
+    if type(commandline) == "table" then
+        proc, err = Astal.Process.subprocessv(commandline)
+    else
+        proc, err = Astal.Process.subprocess(commandline)
+    end
+    if err ~= nil then
+        err(err)
+        return nil
+    end
+    proc.on_stdout = function(_, stdoud)
+        on_stdout(stdoud)
+    end
+    proc.on_stderr = function(_, stderr)
+        on_stderr(stderr)
+    end
+    return proc
+end
+
+---@param commandline string | string[]
+---@return string, string
+function M.exec(commandline)
+    if type(commandline) == "table" then
+        return Astal.Process.execv(commandline)
+    else
+        return Astal.Process.exec(commandline)
+    end
+end
+
+---@param commandline string | string[]
+---@param callback? fun(out: string, err: string): nil
+function M.exec_async(commandline, callback)
+    if callback == nil then
+        callback = function(out, err)
+            if err ~= nil then
+                io.stdout:write(tostring(out) .. "\n")
+            else
+                io.stderr:write(tostring(err) .. "\n")
+            end
+        end
+    end
+
+    if type(commandline) == "table" then
+        Astal.Process.exec_asyncv(commandline, function(_, res)
+            local out, err = Astal.Process.exec_asyncv_finish(res)
+            callback(out, err)
+        end)
+    else
+        Astal.Process.exec_async(commandline, function(_, res)
+            local out, err = Astal.Process.exec_finish(res)
+            callback(out, err)
+        end)
+    end
+end
+
+return M
diff --git a/lang/lua/astal/time.lua b/lang/lua/astal/time.lua
new file mode 100644
index 0000000..7719da9
--- /dev/null
+++ b/lang/lua/astal/time.lua
@@ -0,0 +1,27 @@
+local lgi = require("lgi")
+local Astal = lgi.require("AstalIO", "0.1")
+local GObject = lgi.require("GObject", "2.0")
+
+local M = {}
+
+---@param interval number
+---@param fn function
+---@return { cancel: function, on_now: function }
+function M.interval(interval, fn)
+    return Astal.Time.interval(interval, GObject.Closure(fn))
+end
+
+---@param timeout number
+---@param fn function
+---@return { cancel: function, on_now: function }
+function M.timeout(timeout, fn)
+    return Astal.Time.timeout(timeout, GObject.Closure(fn))
+end
+
+---@param fn function
+---@return { cancel: function, on_now: function }
+function M.idle(fn)
+    return Astal.Time.idle(GObject.Closure(fn))
+end
+
+return M
diff --git a/lang/lua/astal/variable.lua b/lang/lua/astal/variable.lua
new file mode 100644
index 0000000..5a5e169
--- /dev/null
+++ b/lang/lua/astal/variable.lua
@@ -0,0 +1,276 @@
+local lgi = require("lgi")
+local Astal = lgi.require("AstalIO", "0.1")
+local GObject = lgi.require("GObject", "2.0")
+local Binding = require("astal.binding")
+local Time = require("astal.time")
+local Process = require("astal.process")
+
+---@class Variable
+---@field private variable table
+---@field private err_handler? function
+---@field private _value any
+---@field private _poll? table
+---@field private _watch? table
+---@field private poll_interval number
+---@field private poll_exec? string[] | string
+---@field private poll_transform? fun(next: any, prev: any): any
+---@field private poll_fn? function
+---@field private watch_transform? fun(next: any, prev: any): any
+---@field private watch_exec? string[] | string
+local Variable = {}
+Variable.__index = Variable
+
+---@param value any
+---@return Variable
+function Variable.new(value)
+    local v = Astal.VariableBase()
+    local variable = setmetatable({
+        variable = v,
+        _value = value,
+    }, Variable)
+    v.on_dropped = function()
+        variable:stop_watch()
+        variable:stop_watch()
+    end
+    v.on_error = function(_, err)
+        if variable.err_handler then
+            variable.err_handler(err)
+        end
+    end
+    return variable
+end
+
+---@param transform function
+---@return Binding
+function Variable:__call(transform)
+    if transform == nil then
+        transform = function(v)
+            return v
+        end
+        return Binding.new(self)
+    end
+    return Binding.new(self):as(transform)
+end
+
+function Variable:__tostring()
+    return "Variable<" .. tostring(self:get()) .. ">"
+end
+
+function Variable:get()
+    return self._value or nil
+end
+
+function Variable:set(value)
+    if value ~= self:get() then
+        self._value = value
+        self.variable:emit_changed()
+    end
+end
+
+function Variable:start_poll()
+    if self._poll ~= nil then
+        return
+    end
+
+    if self.poll_fn then
+        self._poll = Time.interval(self.poll_interval, function()
+            self:set(self.poll_fn(self:get()))
+        end)
+    elseif self.poll_exec then
+        self._poll = Time.interval(self.poll_interval, function()
+            Process.exec_async(self.poll_exec, function(out, err)
+                if err ~= nil then
+                    return self.variable.emit_error(err)
+                end
+                self:set(self.poll_transform(out, self:get()))
+            end)
+        end)
+    end
+end
+
+function Variable:start_watch()
+    if self._watch then
+        return
+    end
+
+    self._watch = Process.subprocess(self.watch_exec, function(out)
+        self:set(self.watch_transform(out, self:get()))
+    end, function(err)
+        self.variable.emit_error(err)
+    end)
+end
+
+function Variable:stop_poll()
+    if self._poll then
+        self._poll.cancel()
+    end
+    self._poll = nil
+end
+
+function Variable:stop_watch()
+    if self._watch then
+        self._watch.kill()
+    end
+    self._watch = nil
+end
+
+function Variable:is_polling()
+    return self._poll ~= nil
+end
+
+function Variable:is_watching()
+    return self._watch ~= nil
+end
+
+function Variable:drop()
+    self.variable.emit_dropped()
+end
+
+---@param callback function
+---@return Variable
+function Variable:on_dropped(callback)
+    self.variable.on_dropped = callback
+    return self
+end
+
+---@param callback function
+---@return Variable
+function Variable:on_error(callback)
+    self.err_handler = nil
+    self.variable.on_eror = function(_, err)
+        callback(err)
+    end
+    return self
+end
+
+---@param callback fun(value: any)
+---@return function
+function Variable:subscribe(callback)
+    local id = self.variable.on_changed:connect(function()
+        callback(self:get())
+    end)
+    return function()
+        GObject.signal_handler_disconnect(self.variable, id)
+    end
+end
+
+---@param interval number
+---@param exec string | string[] | function
+---@param transform? fun(next: any, prev: any): any
+function Variable:poll(interval, exec, transform)
+    if transform == nil then
+        transform = function(next)
+            return next
+        end
+    end
+    self:stop_poll()
+    self.poll_interval = interval
+    self.poll_transform = transform
+
+    if type(exec) == "function" then
+        self.poll_fn = exec
+        self.poll_exec = nil
+    else
+        self.poll_exec = exec
+        self.poll_fn = nil
+    end
+    self:start_poll()
+    return self
+end
+
+---@param exec string | string[]
+---@param transform? fun(next: any, prev: any): any
+function Variable:watch(exec, transform)
+    if transform == nil then
+        transform = function(next)
+            return next
+        end
+    end
+    self:stop_poll()
+    self.watch_exec = exec
+    self.watch_transform = transform
+    self:start_watch()
+    return self
+end
+
+---@param object table | table[]
+---@param sigOrFn string | fun(...): any
+---@param callback fun(...): any
+---@return Variable
+function Variable:observe(object, sigOrFn, callback)
+    local f
+    if type(sigOrFn) == "function" then
+        f = sigOrFn
+    elseif type(callback) == "function" then
+        f = callback
+    else
+        f = function()
+            return self:get()
+        end
+    end
+    local set = function(...)
+        self:set(f(...))
+    end
+
+    if type(sigOrFn) == "string" then
+        object["on_" .. sigOrFn]:connect(set)
+    else
+        for _, obj in ipairs(object) do
+            obj[1]["on_" .. obj[2]]:connect(set)
+        end
+    end
+    return self
+end
+
+---@param deps Variable | (Binding | Variable)[]
+---@param transform? fun(...): any
+---@return Variable
+function Variable.derive(deps, transform)
+    if type(transform) == "nil" then
+        transform = function(...)
+            return { ... }
+        end
+    end
+
+    if getmetatable(deps) == Variable then
+        local var = Variable.new(transform(deps:get()))
+        deps:subscribe(function(v)
+            var:set(transform(v))
+        end)
+        return var
+    end
+
+    for i, var in ipairs(deps) do
+        if getmetatable(var) == Variable then
+            deps[i] = Binding.new(var)
+        end
+    end
+
+    local update = function()
+        local params = {}
+        for i, binding in ipairs(deps) do
+            params[i] = binding:get()
+        end
+        return transform(table.unpack(params), 1, #deps)
+    end
+
+    local var = Variable.new(update())
+
+    local unsubs = {}
+    for i, b in ipairs(deps) do
+        unsubs[i] = b:subscribe(update)
+    end
+
+    var.variable.on_dropped = function()
+        for _, unsub in ipairs(unsubs) do
+            unsub()
+        end
+    end
+    return var
+end
+
+return setmetatable(Variable, {
+    __call = function(_, v)
+        return Variable.new(v)
+    end,
+})